Mesostructured thin film, mesoporous thin film, and process for production thereof

ABSTRACT

An excellent mesostructured thin film, and a process for producing the mesostructured thin film are provided. In the process, the mesostructured thin film having an oriented rod-like pore structure is formed on a surface of a polymer compound containing a sequence of two or more adjacent methylene groups in the repeating unit of the molecule.

This application is a division of copending application Ser. No.10/670,256, filed Sep. 26, 2003, which, in turn, is a division ofcopending application Ser. No. 09/657,616, filed Sep. 8, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mesostructured thin film, and aprocess for producing the mesostructured thin film. In particular, thepresent invention relates to a mesostructured silica thin film, amesoporous silica thin film, a process for producing the mesostructuredsilica thin film, and a process for producing the mesoporous silica thinfilm.

2. Related Background Art

Porous materials are used in various fields such as adsorption, andseparation. According to IUPAC, the porous materials are classified intomicorporous materials having a pore diameter of less than 2 nm,mesoporous materials having a pore diameter of 2 to 50 nm, andmacroporous materials having a pore diameter of more than 50 nm. Knownmicroporous materials include zeolites such as natural aluminosilicatesand synthetic aluminosilicates, and metal phosphates. These porousmaterials are employed for selective adsorption, shape-selectivecatalytic reactions, molecular-sized reactors, and so forth by utilizingthe fine pore size.

Known microporous crystalline materials have pore diameters of not morethan about 1.5 nm. A solid having a larger pore diameter is demanded foradsorption and reaction of bulkier compounds not adsorbable by themicropore. As the materials having the larger pores, there are knownsilica gels, pillared clays, and the like. However, these materials havea broad pore size distribution, and the pore size cannot readily becontrolled.

With such a background, two methods have been disclosed at about thesame time for synthesizing mesoporous silica having mesopores of auniform size arranged in a honeycomb shape. The one method synthesizes amaterial called MCM-41 by hydrolysis of a silicon alkoxide in thepresence of a surfactant (Nature, vol. 359, p. 710). The other methodsynthesizes a material called FSM-16 by intercalation of analkylammonium in interlaminar spaces of kanemite, a kind of layeredpolysilicate (Journal of Chemical Society, Chemical Communications, vol.1993, p. 680). In both methods, it is considered that surfactantassembly acts as structure-directing agent of mesostructured silica.These substances are useful as a catalyst for bulky molecules whichcannot enter the pores of zeolite, and are promising in application as afunctional material such as optical materials and electronic materials.

In application of such a mesoporous material having a regular porousstructure as a functional material other than catalysts, the techniquefor uniformly holding the material on a substrate is important. Themethod for forming a uniform mesoporous thin film on a substrateincludes a spin coating method as shown in Chemical Communications, vol.1996, p. 1149, and a dip coating method as shown in Nature, vol. 389, p.364, and a deposition method of forming a film on the surface of a solidmaterial by deposition as shown in Nature, vol. 379, p. 703.

SUMMARY OF THE INVENTION

The present invention intends to provide an improved mesostructured thinfilm. The present invention intends also to provide a process forproducing the improved mesostructured thin film.

The process for producing a mesostructured thin film having an orientedrod-like pore structure of the present invention comprises the step offorming the mesostructured thin film on a surface of a polymer compoundcontaining a sequence of two or more adjacent methylene groups in amolecular structure of the repeating unit of the polymer compound.

The process may comprise the step of preparing the surface of thepolymer compound, preferably forming a polymer compound film having thepolymer compound surface on a base plate.

The step of forming the polymer compound surface may be the formation ofa Langmuir-Blodgett film.

The mesostructured thin film is formed on the surface of the polymercompound which has orientation. The orientation is preferably uniaxial.

The mesostructured thin film contains silicon, more specifically silica.Preferably the mesostructured silica thin film is formed by hydrolyzinga silicon alkoxide.

The mesostructured thin film may be formed by hydrolyzing a material forthe mesostructured thin film in the presence of a surfactant. Thesurfactant may be a quaternary alkylammonium, or a surfactant containinga polyethylene oxide as the hydrophilic group.

The process may comprise the step of removing the surfactant after theformation of the mesostructured thin film. By the removal of thesurfactant, the mesostructured thin film can readily be made porous toproduce an excellent mesoporous thin film.

The removal of the surfactant may be conducted by baking themesostructured thin film, or by solvent-extraction of the surfactant.

The mesostructured thin film is formed by hydrolyzing a material for themesostructured thin film, preferably in an acidic condition.

The mesostructured thin film is formed by bringing a solution containinga material for the mesostructured thin film into contact with a surfaceof the polymer compound, specifically by holding the substrate having apolymer compound surface in a solution.

The surface of the polymer compound is preferably subjected to rubbingtreatment before the formation of the mesostructured thin film.Preferably the rubbing treatment is conducted to have orientation,especially uniaxial orientation, to the polymer compound surface. Therubbing treatment is conducted in a direction perpendicular to themesochannel of the mesostructured thin film to be formed.

The number of a sequence of adjacent methylene groups in the repeatingunit of the polymer compound preferably ranges from 2 to 20.

The sequence of the adjacent methylene groups in the repeating unit ofthe polymer compound may be contained either in the main chain or theside chain of the polymer compound.

The mesostructure preferably has a pore structure, and more preferablythe pores in the mesostructure are oriented.

The above constitutions may be combined.

In another embodiment of the present invention, a mesostructured thinfilm having an oriented rod-like pore structure is provided which isformed on a polymer compound containing a sequence of two or moreadjacent methylene groups in a molecular structure of the repeating unitof the polymer compound.

The surface of the polymer compound may be a surface of aLangmuir-Blodgett film of the polymer compound.

The polymer compound is preferably oriented, more preferably uniaxiallyoriented.

The mesostructured thin film contains silicon, specifically silica. Themesostructured thin film is formed preferably by hydrolyzing a siliconalkoxide.

The mesostructured thin film is formed preferably by hydrolysis reactionin the presence of a surfactant.

The mesostructured thin film preferably has a hollow structure.

The surface of the polymer compound is subjected preferably to rubbingtreatment before the formation of the mesostructured thin film.

The rubbing treatment is conducted preferably in a directionperpendicular to mesochannels of the mesostructured thin film to beformed.

The number of a sequence of adjacent methylene groups in the repeatingunit of the polymer compound preferably ranges from 2 to 20.

The sequence of adjacent methylene groups in the repeating unit of thepolymer compound may be contained either in the main chain or the sidechain of the polymer compound.

The mesostructure preferably has a pore structure, and more preferablythe pores are oriented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a TEM image of an oriented silicamesocomplex thin film or a mesoporous thin film prepared in Example 1 ofthe present invention.

FIG. 2 is an explanatory drawing of a reactor for forming a silicamesocomplex thin film of the present invention.

FIGS. 3A and 3B are respectively an explanatory drawing showing themethod of holding the substrate in a reaction solution.

FIG. 4 is a schematic drawing of an LB film forming system employed inthe present invention.

FIG. 5 is a schematic drawing of a microscopic image of a thin filmformed by the reaction for 24 hours in Example 1 of the presentinvention.

FIG. 6 is a drawing showing dependency of diffraction intensity at (110)plane on the in-plane rotation angle in the in-plane X-ray diffractionanalysis of the silica mesostructured thin film formed in Example 1 ofthe present invention.

FIG. 7 is a schematic drawing of a microscope image of a thin filmformed by the reaction for 24 hours in Comparative Example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Conventional methods for producing a mesoporous thin film havedisadvantages below. The mesostructure of a film formed by spin coatingdoes not have a directional configuration throughout the entire film, sothat the pore can not be oriented. The mesostructure of a film formed bydeposition on a substrate depends greatly on the properties of thesubstrate. For the formation of an oriented film by deposition, thesubstrate is limited to those having order at an atomic level like acleavage plane of mica or graphite.

There has been required a technique for the formation of the orientedmesoporous thin film on any substrate. A method to satisfy thisrequirement is disclosed in Chemistry of Materials, vol. 11, p. 1609. Inthis method, a substrate is coated with a thin film of a polymercompound on the surface thereof and the thin film is subjected torubbing treatment.

The examples below show mesostructured thin films and mesoporous thinfilms, formed on a substrate with a simple process, which are oriented,and highly continuous and uniform, and a process for producing the thinfilms.

The present invention is described below in detail.

As an embodiment of the present invention, a process for producing amesostructured silica thin film, and a silica mesostructure produced bythis process are explained below. In the process, using a substratecomprising a polymer compound film that has been subjected to a rubbingtreatment formed on the surface thereof, a mesostructured silica thinfilm is formed on the substrate held in a solution by hydrolysis of asilicon alkoxide under acidic conditions in the presence of asurfactant, wherein the polymer compound has a repeating unit containinga sequence of two or more adjacent methylene groups.

As another embodiment of the present invention, a process for producinga mesostructured silica thin film and a silica mesostructure produced bythis process are explained below. In the process, using a substratecomprising a Langmuir-Blodgett film of a polymer compound formed on thesurface thereof, a mesostructured silica thin film is formed on thesubstrate held in a solution by hydrolysis of a silicon alkoxide underacidic conditions in the presence of a surfactant, wherein the polymercompound has a repeating unit containing a sequence of two or moreadjacent methylene groups.

In the aforementioned two processes, a mesostructured silica thin filmexcellent in uniformity, continuity, and uniaxial orientation can beobtained when the polymer compound has a sequence of adjacent methylenegroups the number of which ranges from 2 to 20 in the repeating unit.The adjacent methylene groups in the repeating unit of the polymercompound may be contained either in the main chain or in the side chainof the polymer compound. The methylene groups contained in the mainchain of the polymer compound tend to improve uniaxial orientation,whereas the methylene groups in the side chain tend to improve thecontinuity of the thin film formed thereon.

In a second invention of the present application, one embodimentprovides a process for producing a hollow mesoporous silica thin film byremoving the surfactant from the mesostructured silica thin film formedas described above, and the mesoporous silica thin film produced by theprocess. The removal of the surfactant is usually conducted by baking,or solvent extraction. However, the method of the removal is not limitedthereto, provided that the surfactant can be removed without destroyingthe mesostructure of the fine pores.

The embodiments of the present invention are explained below.

FIG. 2 is an explanatory drawing of an example of the reactor forforming a silica mesostructured thin film of the present invention. Thematerial consisting of the reactor 21 is not specially limited, providedthat the material is resistant against chemicals, especially acids,including polypropylene and polyfluoroethylene (commercial name:TEFLON). As shown in FIG. 2, for example, an acid-resistant substrateholder 23 is placed in the reactor 21 to hold a substrate 25. A lid 22made of TEFLON polyfluorethylene or a like material seals the reactorwith a seal 24 like an O-ring. In FIG. 2, the substrate 25 is heldhorizontally, but is not limited thereto.

FIGS. 3A and 3B show the method of holding the substrate in a reactionsolution. Generally, as shown in FIG. 3A, the substrate 32 is held in areaction solution 31. However, the substrate 32 may be held on thesurface of the reaction solution with the face 33 having been treatedfor orientation brought into contact with the surface of the reactionsolution to form a similar film. The reactor may be protected by aclosed vessel made of a material of high rigidity against destruction bythe pressure during the reaction.

For use in FIG. 2 and FIGS. 3A and 3B, the reaction solution is anaqueous mixture solution of an alkoxide of silicon such astetraethoxysilane and a surfactant of which pH is adjusted to lower than2 (the isoelectric point of SiO₂) by mixing an acid such as hydrochloricacid. The surfactant is suitably selected from cationic surfactants suchas quaternary alkylammonium salts, and nonionic surfactants having ahydrophilic group such as alkylamine and polyethylene oxide. The lengthof the molecule of the surfactant is selected suitably depending on theintended pore diameter of the mesostructure. An additive such asmesitylene may be added for increasing the micelle diameter of thesurfactant.

The SiO₂ precipitate is formed at a lower rate under acidic conditions,especially near the isoelectric point thereof, although the precipitateis formed instantaneously under basic conditions on addition of thealkoxide.

The substrate employed in the present invention has a thin film of apolymer compound formed thereon and subjected to rubbing treatment. Thebase material for the substrate for forming the polymeric film is notspecially limited, the material including silica glass, ceramics, andresins.

The rubbing treatment is conducted by rubbing with cloth the polymercoat having been formed on a substrate by spin coating or a like coatingmethod. Usually, the rubbing cloth is wound on a roller, and therotating roller is pushed against the surface of the substrate.

The polymer compound for forming the thin film on the surface of thesubstrate has the repeating unit containing a sequence of two or moreadjacent methylene groups. When the repeating unit has the adjacentmethylene groups the number of which ranges from 2 to 20, the filmformed will give a mesostructured silica thin film of excellent uniaxialorientation. It is considered that, within this range of the number ofthe methylene groups, the orientation of the polymer compound impartedby the rubbing is not lost by the elevated reaction temperature indeposition of the mesostructured silica thin film mentioned later.

The specific examples of the polymer compound suitable for the rubbingtreatment are polyimides.

The thickness of the polymer compound thin film is preferably in therange of from 1 to 20 nm, more preferably from 3 to 10 nm.

According to the present invention, the uniaxial orientation of thesilica mesostructure can be obtained also by using a Langmuir-Blodgettfilm (LB film) of a polymer compound in place of the rubbing-treatedpolymer compound thin film. The LB film is prepared by transferring amonomolecular film spread on a water surface onto a substrate. A desirednumber of layers of the film can be obtained by repeating the layerformation. The LB film in the present invention includes built-upmonomolecular films formed on a substrate and heat-treated to change thechemical structure thereof with the built-up structure maintained.

The LB film may be formed by a conventional method. FIG. 4 showsschematically a conventional LB film formation system. In FIG. 4, awater tank 41 is filled with pure water 42. The water tank has a fixedbarrier 43 equipped with a surface pressure sensor not shown in thedrawing. A monomolecular layer 46 is formed by dropping a solutioncontaining the objective substance or the precursor thereof onto thewater surface region between the fixed barrier 43 and a movable barrier44. A surface pressure is applied by moving the movable barrier 44. Themovable barrier 44 is controlled positionally by the surface pressuresensor to apply a prescribed surface pressure during the film formationon the substrate. The fresh pure water is incessantly fed by a watersupply apparatus and a water discharge apparatus not shown in thedrawing. A cavity is provided in a portion of the water tank 41, where abase plate 45 is held. The base plate 45 is driven upward and downwardat a constant speed by a driving mechanism not shown in the drawing. Thefilm on the water surface is transferred onto the base plate during thedownward movement of the base plate into water and during the upwardmovement from the water.

The LB film employed in the present invention is formed, layer by layer,on the base plate with such a system by transferring the monomolecularlayer formed on the water surface by the downward and upward movement ofthe base plate with application of a surface pressure. The condition andthe properties of the film are controlled by the surface pressure, therate of downward and upward movement of the base plate, and the numberof the layers. The surface pressure during the film formation isselected to be optimum from the surface area/surface pressure curve,generally ranging from several mN/m to several ten mN/m. The rate ofmovement of the substrate generally ranges from several mm/min toseveral hundred mm/min. The LB film is generally formed by the methoddescribed above. However, the LB film in the present invention is notlimited thereto, and may be prepared by utilizing flow of the subphasewater.

The base plate for the LB film is not specially limited in its material,but is preferably stable against an acid. The useful material for thebase plate includes silica glass, ceramics, and resins.

The polymer compound for the LB film in the present invention contains asequence of two or more adjacent methylene groups in the repeating unitsimilarly as the compound for the rubbing-treated polymer compound thinfilm. The LB film formed from the compound having 2 to 20 adjacentmethylene groups will give a mesostructured silica thin film ofexcellent uniaxial orientation. The polymer compound having a sequenceof more than 20 adjacent methylene groups in the repeating unit has alower uniaxial orientation. It is considered that, with a larger numberof the methylene groups, the orientation of the polymer compound of theLB film is lost at the elevated reaction temperature in deposition ofthe mesostructured silica thin film.

The polymer-compound suitable for formation of the LB film isexemplified by an alkylamine salt of a polyamic acid, which is heated toform a polyimide LB film on the base plate.

The thickness of the LB film ranges preferably from 1 to 20 nm, morepreferably from 2 to 10 nm.

The mesostructured silica can be deposited on a substrate on theaforementioned conditions. The deposition temperature is not speciallylimited, but is selected preferably in the temperature range from roomtemperature to about 100° C. The reaction time ranges from several hoursto several months. The shorter the reaction time, the thinner will bethe formed film.

The film formed in such a manner on a substrate is washed with purewater and is air-dried to obtain a silica mesocomplex thin film.

From this silica mesocomplex thin film, a mesoporous silica thin film isprepared by removing the template surfactant micelle. The removal of thesurfactant can be conducted by baking or solvent extraction. Forexample, the surfactant can be removed completely by baking themesostructured thin film at 550° C. in the air for 10 hours almostwithout destroying the mesostructure and the uniaxial orientationthereof. Otherwise, solvent extraction is employed for formation of amesoporous thin film on a substrate material nonresistant to baking,although the surfactant cannot be removed completely by the solventextraction.

The gist of the present invention as described above is as follows.Firstly, the continuity of the film can be improved by increasing thehydrophobicity of the polymer compound formed on the base plate andincreasing the deposition density of the mesoporous silica particles onthe rubbing-treated polymer compound thin film or on the LB film.Secondly, a film of highly uniaxial orientation can be prepared bystrengthening the interaction between the alkyl groups on the substratesurface and the alkyl groups of the surfactant molecules.

The present invention is described below in more detail by reference toExamples.

EXAMPLE 1

In this Example, a silica mesocomplex thin film and a mesoporous silicathin film were formed on a substrate having a coat of a polymer compoundthin film containing a sequence of six adjacent methylene groups in therepeating unit in the main chain of the polymer compound and having beensubjected to rubbing treatment.

A silica glass plate for the substrate was washed with acetone,isopropyl alcohol, and pure water successively, and was cleaned with thesurface in an ozone generating apparatus. On this plate, a solution ofpolyamic acid A in NMP was applied by spin coating, and the coatedmatter was baked at 200° C. for one hour to form a polyimide A havingthe structure below:

The thin film was treated with rubbing under the condition shown inTable 1 to prepare the substrate for the mesocomplex silica thin film.TABLE 1 Rubbing Condition of Polyimide A Cloth material Nylon Rollerdiameter (mm) 24 Pushing depth (mm) 0.4 Rotation rate (rpm) 1000 Stagespeed (mm/min) 600 Rotation repetition 2

In 108 mL of pure water, was dissolved 2.82 g of cetyltrimethylammoniumchloride. Thereto, 48.1 mL of 36% hydrochloric acid was added. Themixture was stirred for two hours to prepare an acidic surfactantsolution. To this solution, 1.78 mL of tetraethoxysilane (TEOS) wasadded, and the solution was stirred for 2 minutes and 30 seconds. Thissolution was transferred into a teflon vessel containing theaforementioned substrate as shown in FIG. 2 to hold the substrate in thesolution. This solution contained totally H₂O, HCl,cetyltrimethylammonium chloride, and TEOS at a molar ratio of100:7:0.11:0.10. This vessel was closed with a lid, and the vessel wasplaced in a stainless container. The container was placed in an ovenkept at 80° C. for 24 hours.

Then the substrate that had been in contact with the reaction solutionfor a predetermined time period was taken out from the vessel, washedsufficiently with pure water, and air-dried at room temperature.

The dried substrate after contact with the reaction solution for 24hours was examined by an optical microscopy. FIG. 5 shows schematicallythe observed morphology. As shown in FIG. 5, on the substrate having anoriented polyimide film A that has been subjected to rubbing treatment,an almost continuous film was formed which has a structure 52 of longand narrow domains oriented uniaxially perpendicularly to the rubbingdirection. On this polyimide, the film formed under the conditions ofthis Example had a few defects 51 in a streak shape parallel to therubbing direction as shown in FIG. 5.

This mesostructured silica thin film was observed by X-ray diffractionanalysis to confirm a major diffraction peak assigned to the (100) planeof a hexagonal structure having an interplanar spacing of 3.60 nm.Thereby this thin film was confirmed to have a hexagonal pore structure.The absence of diffraction peak in the wide angle region shows that thesilica constituting the wall is amorphous.

The uniaxial orientation of the mesochannel of the mesostructured silicathin film was evaluated quantitatively by in-plane X-ray diffractionanalysis. The direction of the mesochannel signifies the direction ofdepth of the pores, and the distribution baking, no diffraction peak wasobserved in the wide angle region, which shows that the silica of thewall was kept amorphous. The sample after the baking was confirmed notto contain organic components coming from the surfactant by infraredabsorption spectrum.

The mesoporous silica thin film after the baking was subjected toin-plane X-ray diffraction analysis to determine the dependency of the(110) plane diffraction intensity on the in-plane rotation angle. As theresult, a profile similar to that shown in FIG. 6 was obtained with thehalf width of about 12°. This shows that the uniaxial orientation of themesochannel was kept unchanged after the baking.

The thin film before the baking and the thin film after the baking werecut in the direction parallel to the rubbing direction by means offocused ion beam (FIB), and the sectional faces were observed bytransmission type electron microscopy. In both of the films, thepresence of pores of the hexagonal structure was observed, and theorientation of the mesopores were confirmed to be orientedperpendicularly to the rubbing direction. FIG. 1 shows schematically thecross section of the silica mesocomplex thin film taken in the directionperpendicular to the rubbing direction. In FIG. 1, the numeral 11denotes a silica glass base plate; 12, a rubbing-treated oriented film;13, micelles of a surfactant in a rod shape, or pores; and 14, silica.

The baking treatment improves the adhesion of the mesoporous thin filmto the substrate. Thereby, after the baking, the mesoporous silica filmwas not exfoliated even by hard rubbing of the surface with cloth. Thisis considered to be due to the formation of partial bonding of themesoporous silica layer to the underlaying silica by dehydrationcondensation of silanol.

EXAMPLE 2

In this Example, mesoporous silica was prepared by removing a surfactantfrom a silica mesocomplex formed on a substrate.

On a silica glass base plate, polyimide A was formed, and the polyimideA was subjected to rubbing treatment in the same manner as in Example 1.Thereon, a mesostructured silica thin film was formed with the solutionof the same composition and in the same procedure as in Example 1.

This mesostructured silica thin film was immersed in ethanol at 70° C.for 24 hours for extraction. With this one extraction treatment, 90% ormore of the surfactant was removed from the synthesized silicamesostructure. The same extraction treatment was repeated twice, thereby95% or more of the surfactant being removed. The thin film after theextraction was dried to remove the ethanol to obtain mesoporous silica.

The solvent extraction for the removal of surfactant micelles employedin this Example is effective for removing the surfactant from a silicamesocomplex thin film formed on a substrate having less resistance toheat treatment in an oxidative atmosphere, although the solventextraction is not suitable for complete removal of the surfactant.

The formed mesoporous silica thin film was subjected to in-plane X-raydiffraction analysis as in Example 1 to determine the uniaxialorientation of the mesochannel in the thin film from the in-planerotation dependency of (110) plane diffraction intensity. The obtainedprofile had the same half width as that before the surfactantextraction. This shows that the mesoporous silica thin film could beobtained also by the solvent extraction with the uniaxial orientationretained.

EXAMPLE 3

In this Example, a silica mesocomplex thin film, and a mesoporous silicathin film were formed on a substrate having a coat of a polymer compoundthin film containing a sequence of 17 adjacent methylene groups in therepeating unit in the side chain of the polymer compound and having beensubjected to rubbing treatment.

On a silica glass plate having been preliminarily treated as in Example1, a solution of polyamic acid B in NMP was applied by spin coating, andthe coated matter was baked at 180° C. for one hour to form a polyimideB having the structure below:

The thin film was subjected to rubbing treatment under the conditionshown in Table 2. TABLE 2 Rubbing Condition of Polyimide B Clothmaterial Nylon Roller diameter (mm) 24 Pushing depth (mm) 0.6 Rotationrate (rpm) 1000 Stage speed (mm/min) 600 Rotation repetition 2

This substrate was put into a reaction solution having the samecomposition as in Example 1, and the reaction vessel was placed in anoven kept at 80° C. for 24 hours. Then the substrate was taken out fromthe vessel, washed sufficiently with pure water, and air-dried at roomtemperature.

The dried substrate after contact with the reaction solution for 24hours was observed by optical microscopy to confirm orientation of thetexture. However, the orientation of the texture was unclear incomparison with that observed in Example 1. The orientation direction ofthe texture in the mesostructured silica prepared in this Example wasparallel to the rubbing direction, being different from that inExample 1. The mesostructured silica thin film prepared in this Examplewas completely continuous, and does not have defects like that inExample 1.

This mesostructured silica thin film was observed by X-ray diffractionanalysis to find a major diffraction peak assigned to the (100) plane ofa hexagonal structure having an interplanar spacing of 3.58 nm. Therebythis thin film was confirmed to have a hexagonal pore structure. Theabsence of diffraction peak in the wide angle region shows that thesilica constituting the wall is amorphous.

The uniaxial orientation of the mesochannel of the mesostructured silicathin film was evaluated quantitatively by in-plane X-ray diffractionanalysis as in Example 1. Thereby the dependency of the (110) planediffraction intensity on the in-plane rotation angle was measured.Taking the rubbing direction as the in-plane rotation angle 0°, theprofile is of Gaussian type with the center at 0° with the half width ofabout 35°. This shows that, in the mesostructured silica thin filmprepared in this Example, the mesochannel is oriented nearly parallel tothe rubbing direction.

The substrate having the mesostructured silica thin film was baked underthe same condition as in Example 1. The baking caused no significantchange of the surface condition of the substrate. The X-ray diffractionanalysis of the baked thin film gave an intense diffraction peak at theinterplanar spacing of 3.44 nm, showing the retention of the hexagonalpore structure. After the baking, no diffraction peak was observed inthe wide angle region, which shows that the silica of the wall was keptamorphous. The sample after the baking was confirmed not to containorganic components coming from the surfactant by infrared absorptionspectrum.

The mesoporous silica thin film given by the baking was subjected toin-plane X-ray diffraction analysis to determine the dependency of the(110) plane diffraction intensity on the in-plane rotation angle. As theresult, a profile was of a Gaussian curve with the half width of about340. This shows that the mesostructured silica prepared in this Exampleretained the uniaxial orientation of the mesochannel after the baking.The baking improves the adhesion of the mesostructured thin film to thesubstrate in this Example.

COMPARATIVE EXAMPLE 1

In this Comparative Example, a silica mesocomplex thin film, and amesopourous silica thin film were formed on a substrate having a coat ofa polymer compound thin film having no methylene group in the repeatingunit of the polymer compound and having been subjected to rubbingtreatment.

On a silica glass plate having been treated in the same manner as inExample 1, a solution of polyamic acid C in NMP was applied by spincoating, and the coated matter was baked at 200° C. for one hour to forma polyimide C having the structure below:

The thin film was subjected to rubbing treatment under the conditionshown in Table 3. TABLE 3 Rubbing Condition of Polyimide C Clothmaterial Nylon Roller diameter (mm) 24 Pushing depth (mm) 0.4 Rotationrate (rpm) 1000 Stage speed (mm/min) 600 Rotation repetition 2

This substrate was put into a reaction solution of the same compositionas in Example 1, and the reaction vessel was placed in an oven kept at80° C. for 24 hours. Then the substrate was taken out from the vessel,washed sufficiently with pure water, and air-dried at room temperature.

The mesostructured silica thin film prepared in this Comparative Examplewas observed by optical microscopy. Thereby, long and narrow particlesof mesostructured silica were uniaxially oriented in the rubbingdirection. The particles are in most portions in a scattered state,although distributed continuously in part to form films. FIG. 7 showsschematically the optical microscope image of the mesostructured silicaformed on the substrate in this Comparative Example. In FIG. 7, thebreadth w of the individual particle was in the range from about 2 μm toabout 3 μm. The X-ray diffraction pattern of this sample had adiffraction peak assigned to the (100) plane of the hexagonal structureat the position corresponding to the interplanar spacing of 3.60 nm,showing the formation of the same structure as the mesostructureobtained in Example 1 on the substrate.

The mesochannel was found to be curved at the end portions of theindividual particles shown in FIG. 7, so that the uniaxial orientationof the mesostructured silica prepared in the Comparative Example isinferior as a whole.

EXAMPLE 4

In this Example, a silica mesocomplex thin film, and a mesoporous silicathin film were formed on a substrate coated with an LB film formed fromthe polyimide A employed in Example 1.

Polyamic acid A and N,N-dimethylhexadecylamine were mixed at a molarratio of 1:2 to form a salt of N,N-dimethylhexadecylamine salt of thepolyamic acid A. This salt was dissolved in N,N-dimethylacetamide toform a 0.5 mM solution. This solution was dropped onto a surface ofwater kept at 20° C. in an LB film forming apparatus. The monomolecularfilm formed on the water surface was transferred onto a base plate withapplication of a constant surface pressure of 30 mN/m at a base platedipping speed of 5.4 mm/min.

The employed base plate was a silica glass plate which had been washedwith acetone, isopropyl alcohol, and pure water successively andsubjected to surface cleaning in an ozone generator for hydrophobicity.An LB film of 30 layers of the alkylamine salt of the polyamic acid wasformed on the base plate. The LB film was baked in a nitrogen gas flowat 300° C. for 30 minutes to form an LB film of polyimide A. Imidationby cyclodehydration of polyamic acid and elimination of alkylamine werechecked by infrared spectroscopy.

This obtained substrate was put into a reaction solution having the samecomposition as in Example 1, and the reaction vessel was placed in anoven kept at 80° C. for 24 hours. Then the substrate was taken out fromthe vessel, washed sufficiently with pure water, and air-dried at roomtemperature.

The mesostructured silica thin film formed in this Example was observedby optical microscopy. Thereby, it was found that a continuous film wasformed which had the same texture as that of the thin film prepared inExample 1. The orientation of the texture was in a directionperpendicular to the base plate pull-up direction. The formedmesostructured silica thin film has a few defects in this case also.However, the defects were less than that in the film prepared inExample 1. The method of this Example could give a mesostructure silicathin film having high continuity in comparison with the method in whicha substrate is prepared by forming a film by spin coating on a baseplate and the formed film is rubbed, although the formation of an LBfilm requires much labor.

This mesostructured silica thin film was observed by X-ray diffractionanalysis to find a major diffraction peak assigned to the (100) plane ofa hexagonal structure having an interplanar spacing of 3.58 nm. Therebythis thin film was confirmed to have a hexagonal pore structure. Theabsence of diffraction peak in the wide angle region shows that thesilica constituting the wall is amorphous.

The uniaxial orientation of the mesochannel of the mesostructured silicathin film was evaluated quantitatively by in-plane X-ray diffractionanalysis as in other Examples. Thereby the dependency of the (110) planediffraction intensity on the in-plane rotation angle was measured.Taking the base plate pull-up direction in the LB film formation as thein-plane rotation angle 0°, the profile is of Gaussian type with thecenter at 90° with the half width of about 12°. This shows that, in themesostructured silica thin film formed on the LB film of polyimide A inthis Example, the mesochannel is oriented perpendicularly to thedirection of the movement of the base plate.

The substrate having the mesostructured silica thin film was baked underthe same conditions as in Example 1 to remove the surfactant. The bakingcaused no significant change in the morphology of the film. The X-raydiffraction analysis of the baked thin film gave an intense diffractionpeak at the interplanar spacing of 3.42 nm, showing the retention of thehexagonal pore structure. After the baking, no diffraction peak wasobserved in the wide angle region, which shows that the silica of thewall was kept amorphous. The sample after the baking was confirmed notto contain organic components coming from the surfactant by infraredabsorption spectrum.

The mesoporous silica thin film given by the baking was subjected toin-plane X-ray diffraction analysis to determine the dependency of the(110) plane diffraction intensity on the in-plane rotation angle. As theresult, a profile had a half width of about 12°. This shows that themesostructured silica prepared in this Example retained the uniaxialorientation of the mesochannel after the baking.

EXAMPLE 5

In this Example, a mesostructured silica thin film and a mesoporoussilica thin film having pores of uniaxially oriented two-dimensionalhexagonal structure were formed on a substrate coated with orientedpolyimide A film and subjected to rubbing treatment as in Example 1,using a surfactant having polyethylene oxide group as the hydrophilicgroup.

On a silica glass plate, a thin film of polyimide A was formed with thesame polyamic acid and in the same manner as in Example 1. This thinfilm was subjected to rubbing treatment in the same manner as in Example1 under the conditions shown in Table 1 to obtain the substrate formesostructured silica formation.

5.52 g of polyoxyethylene dodecyl ether (C₁₂H₂₅(CH₂CH₂O)₁₀OH, C₁₂EO₁₀)was dissolved in 129 mL of pure water. Thereto, 20.6 mL of concentratedhydrochloric acid (36%) was added, and further to the solution, 2.20 mLof tetraethoxysilane (TEOS) was added. The mixture was stirred for 3minutes. The total molar ratio of the constituents in the solution ofTEOS, H₂O, HCl, and C₁₂EO₁₀ was 0.1:100:3:0.11.

The above substrate having the rubbing-treated polyimide A film was heldin the above reaction solution with the film-coated face directeddownward. The vessel containing the reaction solution was closedtightly. The reaction was allowed to proceed at 80° C. for three days.During the reaction, the surface was covered via a spacer to obtain anexcellent uniaxially oriented mesostructured silica thin film.

After the contact of the substrate with the reaction solution for theprescribed time, the substrate was taken out from the reaction vessel,washed with pure water sufficiently, and dried in the air at roomtemperature. A continuous film of mesostructured silica was confirmed tobe formed on the substrate.

This film was examined by X-ray diffraction analysis to find a majordiffraction peak corresponding to interplanar spacing of 4.30 nmassigned to the (100) plane of mesostructured silica. This thin film hada pore structure in which rod-like pores are packed hexagonally.

The uniaxial orientation of the mesochannel of the mesostructured silicathin film was also evaluated quantitatively by in-plane X-raydiffraction analysis. From the dependency of the (110) plane diffractionintensity on the in-plane rotation angle, in the mesostructured silicathin film prepared in this Example, the mesochannel is orientedperpendicularly to the rubbing direction with the orientation directiondistribution with the half width of about 20°.

As described above, a uniaxially oriented mesostructured silica thinfilm was confirmed to be formed on the substrate even by use of thenonionic surfactant having polyethylene oxide as the hydrophilic group.

The mesostructured silica thin film was immersed in ethanol and theethanol was refluxed at 70° C. for 24 hours to remove the surfactantfrom the pores in the mesostructured silica. This operation was repeatedtwice. Thereby, 96% or more of the surfactant could be removed from thepores. The thin film after the removal of the surfactant was analyzed byin-plane X-ray diffraction to determine the distribution of poredirection. A mesoporous silica thin film was confirmed to be formed withthe complete retention of the uniaxial orientation with the half widthof about 20°.

The use of a nonionic surfactant having polyethylene oxide as thehydrophilic group makes it possible to control the pore diameter in awide range in comparison with the use of an alkylammonium type ofcationic surfactant.

As shown in the above Examples, a mesocomplex thin film, and amesoporous thin film can be formed with high continuity and highuniaxial orientation on the substrate which has a thin film of a polymercompound having a sequence of two or more adjacent methylene groups inthe repeating unit and has been subjected to rubbing treatment, or onthe substrate which has an LB film of a polymer compound having asequence of two or more adjacent methylene groups in the repeating unit.

According to the present invention, an excellent mesostructured thinfilm can be realized and produced.

1. A process for producing a mesostructured film having an uniaxiallyoriented rod-shaped pore structure, comprising the step of forming themesostructured film on a polymer compound containing a sequence of twoor more adjacent methylene groups in a molecular structure of therepeating unit of the polymer compound, wherein the surface of thepolymer compound is uniaxially oriented.
 2. The process for producing amesostructured film according to claim 1, wherein the process comprisesthe step of preparing the polymer compound.
 3. The process for producinga mesostructured film according to claim 2, wherein the step ofpreparing the polymer compound is the step of forming a film of thepolymer compound on a base plate.
 4. The process for producing amesostructured film according to claim 2, wherein the step of preparingthe polymer compound is the step of forming a Langmuir-Blodgett film asthe film of the polymer compound.
 5. The process for producing amesostructured film according to claim 1, wherein the mesostructuredfilm contains silicon.
 6. The process for producing a mesostructuredfilm according to claim 5, wherein the mesostructured film containssilica.
 7. The process for producing a mesostructured film according toclaim 1, wherein the mesostructured film is formed by hydrolyzing asilicon alkoxide.
 8. The process for producing a mesostructured filmaccording to claim 1, wherein the mesostructured film is formed byhydrolysis reaction in the presence of a surfactant.
 9. The process forproducing a mesostructured film according to claim 8, wherein thesurfactant is a quaternary alkylammonium salt.
 10. The process forproducing a mesostructured film according to claim 8, wherein thesurfactant contains a polyethylene oxide as the hydrophilic group. 11.The process for producing a mesostructured film according to claim 8,further comprising the step of removing the surfactant after forming themesostructured film.
 12. The process for producing a mesostructured filmaccording to claim 11, wherein the step of removing the surfactant isthe step of baking the mesostructured film.
 13. The process forproducing a mesostructured film according to claim 11, wherein the stepof removing the surfactant is the step of removing the surfactant bysolvent-extraction.
 14. The process for producing a mesostructured filmaccording to claim 1, wherein the mesostructured film is formed byhydrolysis reaction under an acidic condition.
 15. The process forproducing a mesostructured film according to claim 1, wherein themesostructured film is formed by bringing a solution containing amaterial for the mesostructured film into contact with a surface of thepolymer compound.
 16. The process for producing a mesostructured filmaccording to claim 1, wherein the number of a sequence of adjacentmethylene groups in the repeating unit of the polymer compound rangesfrom 2 to
 20. 17. The process for producing a mesostructured filmaccording to claim 1, wherein the sequence of adjacent methylene groupsin the repeating unit of the polymer compound is contained in the mainchain of the polymer compound.
 18. The process for producing amesostructured film according to claim 1, wherein the sequence ofadjacent methylene groups in the repeating unit of the polymer compoundis contained in the side chain of the polymer compound.